Characteristics of Momentum Sources and Sinks in Turbulent Channel Flow

The wall-normal gradient of Reynolds shear stress, denoted ∂T+/∂y+, may be thought of as a momentum source or sink term (depending on its sign). This quantity represents a critical driver of the dynamics of wall-turbulence that give rise to the mean velocity distribution. While there have been a number of studies concerning the statistics of ∂T+/∂y+, there remains much to discover regarding the flow features and their interactions that contribute to ∂T+/∂y+. The aim of the present work is to investigate the velocity–vorticity correlations that comprise the Reynolds shear stress gradient. Results show velocity–vorticity correlations rapidly change behaviour up to the location of peak Reynolds shear stress. Beyond this point, the qualitative behaviour remains similar throughout the turbulent flow. Interestingly, it was found from two-point correlations that the mean Reynolds stress gradient at any wall-normal location results from only slight asymmetry in the velocity–vorticity correlations. This suggests that the mean momentum balance is extremely sensitive to the structural features and/or interactions that are responsible for vorticity transport throughout the turbulent layer.